最近几年来，地理信息系统无论是在理论上还是应用上都处在一个飞速发展的阶段。 GIS被应用于多个领域的建模和决策支持，如城市管理、区划、环境整治等等，地理信息成为信息时代重要的组成部分之一； “数字地球”概念的提出，更进一步推动了作为其技术支撑的GIS的发展。 与此同时，一些学者致力于相关的理论研究，如空间感知、空间数据误差、空间关系的形式化等等。 这恰好说明了地理信息系统作为应用技术和学科的两个方面，并且这两个方面构成了相互促进的发展过程。
3.19.1. MongoDB Limit() Method ¶
If you need to read a specified number of data records in MongoDB, you can use the Limit method of MongoDB limit() Method accepts a numeric parameter that specifies the number of records read from the MongoDB.
3.19.2. Grammar ¶
limit() The basic syntax of the method is as follows:
>db.COLLECTION_NAME.find().limit(NUMBER) 3.19.3. Example ¶
The data in the collection col is as follows:
{ "_id" : ObjectId("56066542ade2f21f36b0313a"), "title" : "PHP 教程", "description" : "PHP 是一种创建动态交互性站点的强有力的服务器端脚本语言。", "by" : "菜鸟教程", "url" : "http://www.runoob.com", "tags" : [ "php" ], "likes" : 200 } { "_id" : ObjectId("56066549ade2f21f36b0313b"), "title" : "Java 教程", "description" : "Java 是由Sun Microsystems公司于1995年5月推出的高级程序设计语言。", "by" : "菜鸟教程", "url" : "http://www.runoob.com", "tags" : [ "java" ], "likes" : 150 } { "_id" : ObjectId("5606654fade2f21f36b0313c"), "title" : "MongoDB 教程", "description" : "MongoDB 是一个 Nosql 数据库", "by" : "菜鸟教程", "url" : "http://www.runoob.com", "tags" : [ "mongodb" ], "likes" : 100 } The following example shows two records in the query document:
> db.col.find({},{"title":1,_id:0}).limit(2) { "title" : "PHP 教程" } { "title" : "Java 教程" } > Note: if you do not specify limit() The parameters in the method display all the data in the collection.
3.19.4. MongoDB Skip() Method ¶
In addition to being able to use limit() Method to read a specified amount of data, you can also use the skip() Method to skip the specified amount of data, and the skip method also accepts a numeric parameter as the number of skipped records.
3.19.5. Grammar ¶
skip() The syntax format of method script is as follows:
>db.COLLECTION_NAME.find().limit(NUMBER).skip(NUMBER) 3.19.6. Example ¶
The following example displays only the second document data
>db.col.find({},{"title":1,_id:0}).limit(1).skip(1) { "title" : "Java 教程" } > 注: skip() 方法默认参数为 0 。